The present invention refers to a process and a device for assembly of a prevulcanized annular tread member and a tire casing in view of either the recapping of tires whose tread member is worn, or the production of new tires.
The recapping of tires whose tread member is worn with a prevulcanized annular tread member is well known. U.S. Pat. No. 4,088,521 of Neal describes such an annular tread member with wings fitted on the upper part of the sides of the casing. U.S. Pat. No. 4,957,575 of Cronin reveals a device for assembly through extension of the annular tread member. The annular tread member is supported at its radially interior surface by bars which can spread radially among themselves and thus provide the extension necessary for assembly since such annular tread members have, at rest, a minimum diameter significantly smaller than the maximum outside diameter of the casing.
Such an assembly device presents however several problems. The average extension of the annular tread member is not homogeneous. On the other hand, contact is established between the bars and the radially interior surface of the annular tread member, surface which must then be put in contact with the outside surface of the casing and solidly adhere with it after vulcanization of a cushion gum--the cushion gum being a layer of vulcanizable rubber-based material interposed between the tread and the tire casing. This contact is likely to lead locally to adhesion defects between the annular tread member and the casing which can have later very serious consequences during operation. Finally, the operation of removing these bars after making an initial partial contact of the annular tread member onto the casing can also lead to more or less noticeable global and local misalignment of the annular tread member relative to the casing and thus to uniformity problems of the entire assembly in rotation.